Automatic telephone-exchange system



E. A. MELLINGER AUTOMATIC TELEPHONE EXCHANGE SYSTEM July 27 Filed Jan.l 28. 1908 3 sheetsshe'et 1 mmm Y July 27 1926.

E. A. MELLINGER AUTOMATIC T ELEPHONE EXCHANGE SYSTEM Filed Jan. 28, 1908 3 SheetslStib-e't 2 July 27 1926.

E. A. MELLINGER AUTOMATIC TLPHONE EXCHANGE SYSTEM Fled\ Jan. 28, "1908 .5 Sheets-Sheet 5 Q- 2Mb/WW- Patented July 27, 1926.

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Env/Ann A. runnin-Cinner onions-o, rumors, rvrnsnnnasisinannrs.

`,TO AUTOMATIC ELECTRIC INC., 0F CIICAGO, ILLEEIGS. A GORPORATION- Ol? BELA Application `filed January My invention relates to automatic or semi-,automatic telephone vexchangie systems ,in which ,the exchange apparatus. is controlled b v thesuhscribers or other persons ,overmetallie lines which have no operatingl lgrounds at the substationsthereof, tenis vofthis vlindloeiiig commonlyy known twowiresystems, inasmuch as theoperation of thepexchanpje,apparatus is not dependent upon la,,thirdeonductoin c n Generallvstated theobject ot my inventionis. to provide. an improved and highly etlicientwdwire system of the automatic trunling type. 1, i IQ ,.:Speciallobjects areto provide a two-wire system having no special `high resistance oilsxat tliesubstations thereof; to provide a two-wire systernn which theselectors ,and connectors areeach providedwith onlv one double-wounpdhline relay, `instead ot with a pair of line relays, as hereto't'ore;l to provide ,an,arrangement which the trunk-release is more el'tc'ient than heretofore, the backrelease .ijelayspt the `selectors being` connected in .nnfiltiple or parallel between the battcrvian d ythe trunlrrelefise conductors, where- .bv xthe trunk-release ,circuit 4eiltending' back from vthe connector includestl'le said backleaserelaysin parallel.;y to provide a subscribers individual preliminaryr trunlrinsr switch thatwill automatically.,release and vrestore Iitseltfijl". placed orle'tt ott' normal when the subsoribers line is in normal con- V dition ,to provide an improved` arrangement 1set vforth and claimed.Y

lIn theaccompanying drawings lililsgure l illustrates one of the subscribers stationsv ft anda portioirot the exchange apparatus in a s stem embodying the infinciples of VQ ws aifiotherene oi;

AUTOMATIC rnnnrnionnnxoiianan sir-STEM.

isos. sei-iai No. 413,044.

ers stations A. and a still i'urther portion. of the exchange apparatus. Elias. l anc L taken together illustratean etabiishc'd connection between the subscriband A, the subscriber i't l'ieing' the subscribeixp i i' sin. 3 is an' enlarged view of. the master switch and ot the subscribers individual switch, in which latter his line terminates. The lineswitches arel divided into 2Qjroups, andto each group there is allotted one master switch. Y lli 4 is the preferred arrangement of the master switchbank.

Fig. 5 is a .detail view of the preferred construction oi" impulse-transmitting.,apparatus at the telephone. y y

Fig, 6 shows theterminal apparatus of the trunk-line leading` trom, one'level ot thc banks oi'fthe second-selector switch H, which terminal.apparatus may. be located in a manual board, or in.anysuitableplace. As shown in these drawings, only one tery B, preferably grounded at G, supplies theexchankafe with all ,necessary current for talking' and operating purposes, but. in actual practice this arrangemet may be modi-- lied and a number-ot such batteries may be provided and arranged in any` suitable manner-,that is, one battery may be usedior operatingv one section ot the ,exchange yand another' batterytor operating another section, or a j ilurality of batteries may be made to op- Veratein multiple or in series. bviously, ani-y' combination oit batteries may be employed, deiuentling` upon the conditions to be met..

.its shown, the line oitthe substation ,A terminates in thelineswitch C. This line switch is Shown'more in detail C in F 3. The master switch that cont-role the lective operations of this line switch, and 01" all other line 'switches'ot the same group, is shown at D-inwl1`igslV and rlhe `line switch C is a trunlring switchand= is provid` ed with a plurality of bank jacks whichare assembled to to fin one line switchr bank (not shown). AEach of these bank jacks E is the terminal ot the trunk-line which terminates (as shown in this case) in a first-selector switch F. It will be understood, ot course, thet these bf 'jacks E are l Aiitiple jacksM i ,es' et Lne swt the same group are provided with similar jacks connected to the same trunk-line. It will also be understood that when one line switch is occupying one ot these jacks no other line switch can come in ou the same trunk-line. rllhe tiret-selector F is also a trunking switch, and is provided with sets of bank terminals each oi' which sets terminates in a second selector switch H. EX- actly as the line switch bank jacks are multiple jacks, so the first-selector bank terminals are multiple terminals. The lirstselector switches, following the general arrangement oi a system in which automatic trunking switches are arranged on the percentage basis, are arranged in groups, and each switch of a group is, ot' course, provided with a multiple contact tor each trunk-line, so that all ot the lirstselectors of the group to which the lirstselector F belongs have access to the saine second-selectors. n a similar manner the second-selector H is provided with multiple bank terminals to which are connected trunk-lines that terminate in connectors, one of which latter is shown at l. Ot course, the line switch C allot-ted to the substation A is the same as the line switch C. ln order that this system may be more easily understood, the various mechanisms vill first be described in detail as to their mechanical features, and atter this is done the circuits will be carefully pointed out by describing the process by which one subscriber calls another subscriber. The subscribers station apparatus is ot the general type which is now in use in such places as Grand Rapids, Mich., Los Angeles, Calit.,etc.,but is improved upon in certain respects, mainly to adapt it to the telephone system herein disclosed. As shown. this substation comprises the usual receiver 2, transmitter 3, inductioncoil fl, ringer 5, switch-hook 6 and impulse wheel 7. The said impulse wheel 7 is mounted upon the shaft 8 which extends through the telephone, and said shaft is pro- *ided with al dial (not shown) which is mounted on the end behind the impulse wheel (considering the phone shown in Fig. 1). Said dial is provided with the usual .tinger holes suitably marked with numerals or letters to guide the subscriber in making` a call. Associated with this dial there is also the usual linger stop .(not shown) to determine the limit ot the downward movement o't the dial each time that it is rotated.

in accordance with some digit. The impulse wheel is provided on its periphery with a set ot suitable impulse teeth 9 which are twisted out of the plane of the impulse wheel For the purpose ot' obliqnely engaging the lug 10 on the impulse spring 1l, whereby the said spring 11 may be separated 'from the spring 12 a proper number of tin'ies as the impulse wheel 7 returns to its normal position. It will be understood, oi' course, that in connection with this impulse wheel there is provided a suitable clock-spring (not shown) which is adapted to be wound up each time the subscriber pulls down the dial, and which constitutes the means for returning the impuls-e wheel to its normal position each time. lt will also be understood that a suitable stop (not shown) is provided to limit the return movement o'l said impulse wheel. Ot course, the induction-coil. l is provided with primary and secondary windings 13 and 14, respectively. As this is a common battery system the transmitter 3 in series with the primary winding 13 are bridged across the line conductors when the subscribers are talking. rl`he receiver 2 is in a closed local circuit, in series with the secondary winding 14. The switch-hook G is not only used tor holding the receiver 2, as is ordinarily the case, but is also adapted for switching the spring 15 back and forth between the springs 16 and 17, so that when the receiver is on the switch-hook-that is. when the switch-hook is down-the springs 15 and 17 are maintained in contact tor the purpose ot bridging the ringer 5 in series with the condenser 18 across the line; but when the receiver is ott the switch-hook-v that is, when the switch-hook is up-tlie springs 15 and 16 are brought into contact for the purpose of closing the talking circuit. Although the arrangement ot' the springs shown at substation A (Fig. 1) may be employed, a preferred arrangement ot the springs is shown in Fig. 5. rlfhe spring 11 is not directly operated by the impulse wheel 7, but in place thereof an extra spring 11a is provided which is equipped with the lug l0 and is directly engaged by the impulse wheel 7, so that on the return motion ot the impulse wheel the spi-infr 11 is separated trom the spring 12 by the action of the spring 11, preferably through an insulating member 11".

The line switch C, which is allotted exclusively to a subscriber (see llig. 3), is a simple mechanism comprising the so-called trip magnet 19, the release magnet 2O and the bridge-cut-oii7 relay 21. These magnets may be mounted on any suitable trame. @if course, said magnets should be properly mounted and raised. fait enough from the trame to insure the proper operation ot their armatures, springs and other details which these arn'iatures control. As shown, the cutoii relay 21 is provided with cut-oil relay springs 22, 23, 24 and 25. These springs are so arranged that normally the springs 22 and 23 are in contact and the springs 24; and 25 are also in contact. Furthermore, when the magnet 21 operatively energizes, the said springs are separated as shown. The release magnettlninst also'be `fraisedfsfuiii`eiently to permit t-liei ,operation3v of l'air armai-tum23y 'suiti ably* pivot-Jed l*at v"af 'point 2Ti Thisarinature is, orf-course," provided?'Withf-afv retraeting spring 23 which' normally retains!thesaid armature 'againstI the" stop 2.9i Asi-ndi@ cated, this iari'nature carries at'its forward end, andl pivotalll'y `mountedthereon, the arm.v 30 of thetripinagnet19.1Also mounted on'- the' samet '-lrame, and 1in about the Vposi-tion show-1i frel'ative yto the` trip and release-mage nets .19 and 20, i'sf these-called plunger arm 31\vl1ich is pi'vot'ally lsecured v'toi the* frame by the pin 32.*if'Thi`s-arml is provided "onf the side f'nearest therelease magnet! 20 with spring' `33fperinanently` secured 5to saidv arm 31st or 'about its riglitjextremity. Asfindii cated, this spring extends tio thele'ft'over the point 324th-atis', between the point 32 and therel'easevniagnet 2(1V The le'teIid'ol'f this-'spring 33is'treefrom thegarm 31, Vand is'rec'eive'd by a link 34 which is hungto a suitable meinber'35 securedn'to the 'forward end i' th'e'arm 30,' as'shcwn; It Will bef'seen, therefore', that owing to the link 34' the spring 33 isretained under tension 'andtends' to rotat'efthearm 31abot`1tthe pivot 32 in tit-clockwise direction.' @n the-left extremity of the *arm 31 thereis fastened hard steel plate 36 Which'sli'ghtl'y overlapsesaid arm.' Also, the arm 30 carries on its upper end and opposit'ethi'sv plate 36 av corresponding hardsteel plate 37.-" The arm 31 isy normally retained in aposition-` VWith'themember 36 under the inemberBT-and islatchedthereby. In'addition;theai'm `31 islequipped on its right endv With a'i plunger 38 having a faire like upper section 39fprovided 'Withlaslot 40, as shoWn.- Thisfanllikesection 39 is de# vsignedf'ioi' operating :in conjunction `with ra so-called plunger 'shaft41which is con` trolled by the master switch D. Thisshatt 41 operates back and forth" about an axis through thecenter 42. -'Theplunger 33^rests f against theshaft 41,3 engaginglthe'ridge143 Which extends along the :length ofsaid lsha-ft by the slot 40. The plunger 38, isy therefore,

normally swung'bacl and `forth by' the"` slot 41 aboi'it'thepivot 44; f As shown', thel'oWe-r end of theplunger 33 carries an'in'su'lating member 45'mounted on laVsmallipin 46.' As shown inthe drawings, the plunger and; therefore, the pin4 46 Avare 'distortedfrom their true positions', -as is 'also theleaseavith the springs47', 43, 49; 50, 51-, 52, v53and 54. These 'parts are showndiagramniaticalzly. and not in theirtrue positions in ordeiwfthat' the circuits may-bc more easilyunderstood. The

actual construction is. ofweourseg' `obvious fromv the explanation 'givenof theeb'ack-:and- Ylorth emotion. Als 'already eitplained, the banket' the line switch-C1comprises;a group of bank jacks .Tl,"u-sually `teni .in number. These bank, j aeks: are' arranged inthe' "are` ot -la= circuit te contorniV wvthfthefsavingng meH tion of thefplunger3'8,'so tha-tlthe" distance between themember 45 and the bank springs is constant, nounatter )what the 'position-ot the`= plunger 38l 'may be. ,The operation ot theline' switclr@ 'isfin general as' follows: Zhen theztrip magnet 19' attracts the armature 30` the plate 3Tslips oli" troniY the' plate 36,an'd the spring 33 then causes the plunger arm 31tofrotate, so as to thrust. tlieplunger 38v onto the bank-jaek'opposite which itis located kat thetime, as shown; fiter-theplunger arm thus operates,theI plunger shaft 41 of; coursey continues its backland-'forth 'motioin regardless of theoper'ation `of the plunger 38. i After l`thus* being operated, the line sivitch C may .be restored by energizing the release magnet- 20, Which'latter attracts its armature 26, 'thereby' raising the trip arma y ture 30 to 'ai height su'iiicie'nt 'to enable the plate 3'? 'to be drawn over the plate 36 by thertensionmc the spring '33; Then When the magnet- /IOdeenergizes, the spring 28v restores the'plunger 38V te engagement with the plunger'lshaft 41. As indicated by the dotted'lines,it Will beseen that if thevsha'ft 41 has notY bytlrat time returned t0 theffposition it originally held"W'hen theplunger 38 left theridge` 43,V 'the plunger 38 Will not return into 'locked engagementpwith the'said ridgeuntil suclrtime as theshatt 41 vshall havereturned tosuch position. It 'makes no difference, of course, Whether' the kshaft 41 is traveling-` oneE Way or theother; lVhenever the ,ridge43 passes over the notch 40v7 after the .plunger 33-has been Withdrawn from thebank, the locking: engagement described: .willthus take place E'and from .thence on tliefpl-ungerSS Willcontinueto oscillate back and.' orthgtogether With `theshaft 41. During thexinterval betweenrthe time when the plunger 38 is released andY the time the lcking engagement occurs the plunger v38 will remain stationary andopposite the bank jackla'St'uSed:v and if in the meantimethe subscriber fagain makes a` callf'then the plunger 33 ``-will Aseize ton the sametrunklike. #It is v.to be :understood'thatthe springs 4S andQ of each bank Y.ja-ck* are separated by' suitable insulating material Which is made; with a recess, so that WhileV the-plunger is in engagementwith vthe banks (as shoWn in full lines in* Fig. 3), or While itisin'sliding engagement Withthe plunger.shaiftr41 (as shown bythe'dottedlines in Fig) `the plunger 33 is'heldxagainst turning, because the tip fo'fthe'f plunger 38 isA notraisedfsuiJA nciently toy clear` the said recess." It is only .When the; plungers are in locking engagef nient -With,the'shaft; that the tips of the lplungers -33`suiiiciently clear this insulating material to be able to rotate. j

The; means provided for "oscillating the p'luligerfshaft. `41v is the 'master switch` D. Thisl master 4-switch is' also. la Vcemp'aratively simple deviee,-censisting et an .nterrupteii magnet 55 and the interrupter relay 56. This master switch may be mounted upon a frame similar to that described for the linel switch C, care being taken that the magnets 55 and 56 are raised high enough to permit thesaid magnets to operate withoutinterference. The magnet 56 is simply a relay controlling the springs 57 and 58 which are in the energizing circuit for the interrupter magnet 5:7. rl`he said interrupter magnet 55 may be of any suitable character, such as the one described in United States Letters Patent No. 831,875, granted September 2:3, 1906 to Alexander E. Keith; but the one herein shown like the one described in United States Letters Patent No. 841,004, granted January 8, 1907, to John Erickson. rIhis interrupter includes the interrupter springs 59 and 60 and the locking spring 61. These springs are controlled by the interrupter armature 62, which latter carries on its end a pswl 63 for operating the ratchet wheel 64. This ratchet wheel is mounted on an axle 65 perpendicular to the base, and is provided on one side with a plurality of pins 66. These pins are for the purpose of operating a cam 67 which is rigidly secured to the plunger shaft 41. Jalso secured to the said shaft and cam there is a wiper 68 adapted to sweep over the master switch bank contacts c andthe common member 69, in such a manner that one of the contacts a is always maintained in electrical connection with the said member 69. The purpose of the interrupter magnet 65 is to rotate the ratchet wheel 64 in a counter-clockwise direction; rlhis wheel is in addition provided with a stop-pawl 7 O to prevent clockwise rotation. It will be seen, therefore, that with this construction while the interrupter magnet 55 operates, the ratchet wheel 64 will be rotated and the shaft 4l and wiper 68 will be advanced step by step until one of the pins 66, clears the cam 67, at which instant said cam is allowed to spring into engagenien with thc next succeeding pin. The eiffect of this operation is that the wiper 68 and shaft 41 will advance step by step in one direction and spring hack over all of the previously passed contacts by one jump. A preferred arrangement of the master switch bank, as already stated, is shown in Fig. 4, and when the wiper leaves the neat to the last contact 71 the wiper 68 clears an insulated spring 72 over which it slides at the return jump instead of passing over the contacts a. It will be seen that when the wiper 68 arrives opposite the first contact 73, the wiper 68 again `iumps into engagement with the said first contact 7 3. lt will be seen, therefore, that the position of the wiper 68 relative to the bank contacts a shows the position of all plungers that are in locked engagement with the plunger shaft 41.. lt will be assumed, that when the wiper 68 is opd releasing relay.

posite the tirst contact 73 all plungers in locked engagement with the plunger shaft will be foundv opposite the multiple bank jacks which are terminals of the trunk-line leading to the 61st-selector F. Therefore, the plunger 38 if thus locked will be opposite the bank 'jack E. As shown in Fig. 1, every trunk-line leading from the line switch banks, such as the one terminating in the tiret-selector F and comprising the conductors 74 and 75, is provided with means for automatically releasing the line switch C whenever the subscribers line is ope-ned after the switch has been operated. This means comprises a double-wound relay 76 having windings 7 7 and 78 and a relay 79 for controlling the circuit through the commutator interrupter 80.

The first-selector F is a modified form of the selector switch disclosed in United States Letters Patent No. 815,321, granted March 18, 1906, to Keith, Erickson & Erickson* that is, it is a modifi-ed form as tar the circuits are concerned, the mechanical aspect of the switch being the same with one exception, namely in the patent to which reference is made the release magnet does not produce the release until it deenergizes, but in the first-selector of my present invention this release has been changed to the form described in United States Letters Patent No. 815,176, also granted March 13, 1906, to Keith, Erickson Sa Erickson. The release is such that as soon'as the release magnet ener gizes, the connector switch shaft and side switch are restoret. For example, the switch F is provided with a switch shaft (not shown) which carries the line and private wipers 81 and 82, and 83. Instead of: having two line relays, as is ordinarily the case, this selector is provided with one double-wound line relay 84. ln addition, the said selector comprises a slow-acting relay 85 known as the private magnet relay, and another slow-acting relay 86 known as the The vertical magnet 87, the rotary magnet 88, the release magnet 89 and the private magnet 90 are well known and in general operate the same as the magnets of the selector patent. The said private magnet, of course, controls the side switch wipers 91, 92, 93 and 94. These relaysI may be made slow-acting in any manner known to the art` for Xample, by providing each relay with an additional low-resistance winding closed upon itself, or by providing each relay with a copper shield, which copper shield is iudicated in the drawings by the small squares at the top of the coils.

` The first-selector H is substantially the same as the lirstselector F. It is equipped with the same number of magnets, namely the line relay 95, the private magnet 96, thc 'releasing relay the release mag it 98, the vertical magnet 99, :rotary man t 1G() and the iprivate'inagnet 101.1 The circuits, howeyerp are trifle. vdifferentiat certain points, Which differences v villbe explained hereinafter: p

The :connector switch 1 is nioditied 'torni ot the connecter switch disclcsed in Un l StatesLetters Patent lilo. 815,1?6, grin d March, 13 1906, toKeith, Erickson t Erickson. ,lts modilication rel-etes mainly to the circuits-*the mechanical i; itures ci the con nector switchul being practically the saine as those ofthe cbnnecter et the said patent. Forceirainplc, the connector switch l is provided\vith the usual switch shalt (not shown-)f that carries the' line and private wip`ers12 and103, andlOl. Like the selector-sl? andH, the connector switch l instead of -having `twolinewrelays, ,as is usually the case/is provided With'one double-Wound relay 105.V It also yhas a slow-acting; relay 106 known as the release relay, and another slowactingrelaylOf known as the private niagnetrelay.; 'ThisY relay .also controls the busy circuit andthe circuit of the Wellknoivn rotary 1na,qnet.109. The vertical magnet 110, the release Inagnetlli, the ringer relay 112 the private magnet 113 and the baalt-bridge relay. 1.121 are Well known.VA It will be' seen that` the connectorisalso provided with the usual eondensersll and 116 which are included in the talking circuit` and which oividefthe said talking` circuit into,inductivelyT connectedsections. At the exchange there is valso provided a ringergenerator 11?, a coinlniitator,circuit interrupter. 118 'tor controllingthe ringer relay circuit, a busy transiforinerf119, and aconnnutator circuit interr'upter h1120 .for the .busy transformer. it will bex evident, oi'coursmthat it it is desired these coinniutator interrupters 118 and 120 may be consolidated into one.

The `line-switch C being the saine` as the line switch C. the release .magnet 121, the trip niagnet 122, :and the cut-oft4 relay 1" ,LADO ivill, oi course, .be recognised; At the e15- change4 there is also provided a coininon. relay 121i- '.(Fig': 1) for the purpose of supervision,and.toindicate to the exchange attendant .Whenever a. subscrlbefs` line is grounded. LA lsiniilar relay 125 is shown in connection Withthe line srvitelrC. ,These relays*mayI befallottedone to each group ot' subscribers or one to each of the subscribers. `Whenenergized they.V are adapted toclose alsigi'ial circuit ot'any character, such as bell, lainp, or both..

"Having thus described 'the general character of,the-apparatus which is used in the system l will noiv describe the process by whichthe'callingsubscriber A. (Figpl) es` tablishes connection, signals and converses With the subscriber at substation A 2), and also the niethod by `lwhich the apparatus isy restored.to'norinal condition after being; brought into use.` Assuming this to be aten-thousand subscriber system, the sub- 'station A will be designated as and Iin order to call the said 'substation the subscriber at substation A inust operate his 4dial tour tinies in accordance with the digits 42, 2, 2 and 0.: As socn as the subscriber reinoves his receiver 2 the switclrhock 6 is permitted to rise, Wherebythe springs 15 Aand 1G are bi'foughtinto Contact. rThe circuit is thereby closed, including` .the 7trip ,magnet 19 and the connncn relay 1241-. A Said circuit extends troni ground G1 through the trip magnetL 19., and through the cut-oft relay springs and 2a to the rotary line con- 'ductor125, thence throughr the springs 15 andvl, and through the interrupter springs 12 and 11, through the transmitter 8 tothe yvertical line conductor 127, thence through the cut-oil relay spri1'igs-22 and and the relay 1211 to the batterylead 128thencc through battery B te ground G. The tripv magnet 19 then attracts its armature 30 (see Fig. ,3), thereby causing the plunger 38 to tri/p onto a bank jackV E, assuming` that the plunger 38 is opposite the said bank jack at the tinie. As soon as this plunger operates, as described, itpresses `the bank springs bei and 53, and 49, 47 and L18, and 52-and51 into contact. The {closure ot' contact between the springs if? and Li8, it will be seen, closes an enrgizvi-ng circuit through the bri'dggjccut-oiln relay 21 which entends troni ground G2 through 'the springs fr? and 18, conductor 129, through the relay 21 tothe battery lead 128, thencevthrough battery B to `round Cw The' cut-oil relay thus ,separates the cut-off relay springs, 'thereby breaking;l the. originally' established circuit through the trip magnet 19 and the coininon .relay 12a.4 Attention Will be calledt-othe tact that this operation is so quick-.that is, the trippingoperation of the `line switch C-that the relay 124 remains energized `but for a very short interval rct'tiine, and too short for establishing1 an alarin of the character described in the preceding explanation. The closure of contact between the bank springs and t53 extends the subscribers vertical line conductor 127 into `contact With the trunk conductor 7st., and the closure ot contact betuf'een the bank springs 52 and 51 places the rotary line conductor 126 in contact with the rotary trunk conductor 75, As a result an energizing circuit is established through the line relay S45i et therst-selecter l?. This energising circuit stende trein `Qroiuid G3 through the Winding1 130 ot' the line relay te, contact point 131, side switch Wiper 92, trai k conductor 'Z winding 78 of the trun relay 76, bank springs 51 and 52'to the rotary .line cenducterm thence through ,he ter over the springs and 53, through the rind f W the trunk relay 7G te the 4 .f trunk cene ter 7,4, thence through the side substation .er to :the vertical line conducswitch wiper 91, contact point 132, winding 133 of the line relay 84 to the battery lead 128, thence through battery B to ground G. The closure of this circuit causes the line relay 84 to energize, the windings 130 and 133 being` in series, whereby the spring 134 is separated from the spring 135 and carried into engagement with the spring 136, with the result that the slow-acting releasing relay 86 energizes and in turn operates to shift the spring` 137 from the spring- 138 and into engagement with the spring 139. The energizing circuit for the slow-acting` relay 86 extends from ground G4 through the line relay springs 134 and 136, through the said relay 86 to the battery lead 128, thence4 through battery B to ground Gr. lt will be understood that the relays spoken of as slow-acting relays in this specification are slow-acting only as far as cle-energizing is concerned. These slow-acting relays are capable of energizing almost as quickly as the other relays. lhen the line relay 84 energizes, as described, the line relay spring 135 l it will be seen, is placed in connection with the slow-acting private magnet rela-y 85, and through the said relay with the vertical magnet 87, whereby ground impulses may be sent from the said spring 135 through the said magnets 85 and 87 while the relay 86 is energized. Attention is called to the fact that the trunk relay 77 is a slow-acting relay and energizes at the same time that the line relay 84 energizes and over the same circuit. This relay, therefore, operates when connection is established with the selector F, as described, to separate the springs 140 and 141. The foregoing having been accomplished by the subscriber in theJ act of removing` his receiver from the switchhook, he then Continues the call by operating his 'dial for the first digit 2.

lVhen the dial is drawn down the impulse wheel 7 is rotated so that two of the impulse teeth 9 are carried beyond the lug 10 on the spring 11; then as the da] returns, the said teeth operate to twice separate the spring 11 from the spring 12. Each time that the said springs are separated the energizing circuit for the relays 77 and 84 is interrupted; but since the relay 77 is slowacting the said relay is not given time to (lc-energize between impulses. 1t is to be understood that the impulse wheel 7 operates at such a rate as to produce such a result. In this system the subscribers are instructed that when the dial is drawn down it should be absolutely released and allowed tc return unimpeded, or if desired a telephone with a protected dial, such as the one described in the application of John Erickson, Serial No. 331,700, filed August 23, 1906, may be used. Each time that the circuit is interrupted at the springs 11 and 12, as described, the armature of the line relay 84 of the selector F falls back and permits the spring 134 to come into contact with the spring 135, and impulses are transmitted from ground G4 by way of the springs 134 and 135 of the line relay, and the springs 137 and 139 of the slow-acting release relay 86, through the private magnet relay 85 and through the vertical magnet 87 to the side switch contact point 142, thence over the side switch Wiper 94 to the battery lead 128, thence through battery B to ground G. As already explained, the trunk relay 77 does not have time to deenergize while the line relay 84 is operated, and the same is true of the release relay 86. This relay 86 is so built that the customary interruptions of the circuit at the point between the line springs 134 and 136 are not of sufficient duration to permit the said relay 86 to be cle-energized. The first impulse transmitted by the line relay 84 over the circuit described causes the private magnet relay 85 to energize, and said relay remains so during the succeeding impulses owingl to its slow-acting character. Upon energizing, the said slow-acting relay 85 presses the springs 143 and 144 into contact, whereby the private magnet 90 is energized by a flow of current from ground G1 through said springs 143 and 144, and through the said private magnet 90 to the battery lead 128, thence through battery B to ground G. The said private magnet 90, of course, remains energized as long as the slow-acting relay 85 is energized. The impulses produced by the line relay 84, of course, also energize the vertical magnet 87, which vertical magnet 87 then operates to raise the switch shaft one step for each impulse. Since two impulses are transmitted to the shaft, the vertical, line and private wipers 81., 82 and 83 are raised two steps and brought opposite the first contacts of the second bank level of the selector F. It will be seen that when the impulse wheel 7 ceases to operate the spring 11, the line relay 84 again resumes its constant energized condition, so that the private magnet relay 85 de-energizes, whereby the springs 143 and 144 are allowed to separate. and the private magnet 90 as a result allowed to cle-energize, which private magnet then allows the side switch to trip to second position. As soon as the side switch trips to second position the side switch wiper 94 engages the Contact point 145, thereby establishing an energizing circuit for the rotary magnet 88 extending from ground G3 through the interrupter spring 146, through the rotary magnet 88 to the contact point 145, thence through the side switch wiper 94 to the battery lead 128, and through battery B to ground G. The rotary magnet then attracts its armature, rotating the shaft one step and thus causing the line wipers to engage' 'the' contacts of the first trunk-line in' the` second' level. The' inter rupter'used `in 'connection' with this rotary magnet may' be 'of any suitable character, but :preferably it is ot the character shown and 'described in said letters Patent `No 341,004 and No. 831,875.V As disclosed in s aid'selector"l3atent No. '315,321, when'the rotary'fmagnet 88" attracts`its armaturethe armature o't'the private' magnet 90' is' operated at'thesame tin'iebyt'he usual `private' armature ringer carried by the rotary armature 'lhe'result 'is that-fthe first step or operation of the rotary magnet'not only 1ota'tes\'tlie^shatt` wipers' into vengagement withthe' iirst"trunl -line,"but as the rotary armature'falls 'back the private armature is also'permitted to tall back, vat which time the sideswitch trips tol'third position. This is onlytrue it the first trunk is' idle, which tr'unl, it Lis"assumed, terminates in the second-selector H'. l'It will befseen that when the side switch passes to third position the side `switch wiper' 93 'eng-ages the'contact point 149, whereby the private wiper 83 pla-ced lin coni're'ction with lground G, since'fthe 'line 'relay' 311 isI energized; The circuitover'which this' connection is maintaiued'fis asv tollowsz" from ground 'G1 through theiine'relay''springs 134 and 136, cont u'c'toi" 150 to"'the contact point 1419, thence to'the side switch wiper' 93 and over the conductor 14715' the private wiper`83.` The private wiper 83 being in' engagement with' onef'of the multiple private vbankv contacts cires'ponding toV the trimk-line terminating in'the Isele'ctoi H, all of the multiple privatev bankfcoiitacts `connected there* to ar'e"`tlius providedwith afguarding'potenialI for' preventin'gjl other' selectors from ringing' the'l'saine trunk-line."` It the `first trunk Ais'busy, how'everfthe"armature of the private magnet does not-fallback with therotar'yarmature at the end ot the first step but is retained by` the private magnet which -is vthen 'energized by atlow of current over. a 'circuiti'vhi'chi's closed `asgsoon as theprlvate-wiper 83 engagesa groundedV contact', whereby an"ene'1'gizi1ig 'circuit is set up thiougli the'- private magnet 9() eX- tefndi'ng "fromlthiis grounded private bankv contact through thefwiper 83","over the conductor"`1t7 to' the sideswitch wiper 93,

'then'c'e to' thefcontact point 148, andthro'ugh the private'magnet' 90 to'the battery lead 128, thence' throughfbattery B to ground G.v

it will be seen, therefore), that the Vprivate magnet will retain the 'side switch locked in secondposition as'longy as the private wiper' 83 encounters busy vtrunk-lines, on ac-` count o ii the' connectionv maintained between eachpri'vate bank' contact of 'a busy line and groundfV '1-Ioweve`r, as vlsoon as the 'rotary magnet 88 advances the wipers onto anidle' trunk-line, the energizing vc1rcu1t for the pri'- permitting the side switch to pass to third l position. `Assoon as 'the side switch passes to third' position a guarding potential 'is esi tablished at the private wiper S3 and, theretore, 'at all private banl: multiple contacts, as already efq'alained.V It will be assumed that the Erst-selector' F stops on the first trunk-line,v as previously explained.; then when the side switch passes to third 'p'osi tien the side' switch wipers 91 and 92,' up# on engaging the third-position contacts 151 and 152, respectively, extend the trunk conductors 'TA1' and 7 5 to the trunk conductors and 15e which terminate in the secondselector H. It will be evident that'f'whe'n' the side switch of the liistselect'or'is' tiret position the wipers 91, 92,' 93land 94 are in 'engagement with the contact points 132, 131, 155 and`142; when in secondpd sition they are in engagement with theco'ntact points' 156, 157,148' and 145'; landwhen in third'fposition the wipers are in engagement with the Contact 'points '151, 152,149 and 158. It will be seen that when the side switch thus passes' to third"`positio`n the energizing circuit torthe 'lin'er'e'lay 84 ot the selector F is cu't off and, therefore, the said relay is restored. It will 'be seen, of course, that theene'rgiz'ing circuit for thev line relay 84 cannot be brokenuntil the" side switch 'passes tothird position, be# cause the side vitch contact pointsl 132 and 15 5` are connected onf'one side', and the side switchcontact'points 131`and 157 are likewise connected onv th'e other' side. It iollows', therefore, that'the connectionfto ground'G4 is 'interrupted at a point between the line relay springs 1311` and 13:6,"and a guarding potential l is established at the private blank contact ven,g'a0e'cl` by the private wiper83"fromthe selector H, as fol-v lows: As soon as the' side' switch trips to third' position, as explained,l the Vline rel'ay like` the' line relay 84, energizesv over the'ollowing Y circuit: 'from ground G5" through theyfinding 159 of'the` relay 95,A to the si'de yswitch wiper 1GO of the 'secondselector H, thence'to the trunk conductor' 154, rotary line 'wiper 82 of the 'second-v select'or F, contact point 152, side'vswitch wiper 92, through th'e` substation A,`back on the4 otherlside of the line rto the first-- selector side switch wiper 91, contact point 151, vertical line wiper 81 to' the'side switch wiper `161 ot the second-selector H, thence through the'winding 162 oi the line"rela'y to the battery lead 128, 'thencethrough battery B tolground GJA The line' relay 95 being sii'niiar tothe line 'relay 84,'the spring' 163 is separated from Ytbespring 164 and carriedonto the springl'. As' a result lim the slow-acting release relay 97 is energized by a tlow ot' current from ground GG through the springs 168 and 165, release relay 97 to the battery lead 128, thence through battery B to ground G.

The slow-acting relay 97, upon operating, shifts the spring 166 from the spring 167 into contact with the spring 168, similar to the slow-acting relay 86. rlhis relay 97, however, has two additional springs 169 and 170 which are pressed into contact at the same time, whereby a ground connection is substituted at the private wiper 83 trom the ground G7 in place of the ground G1. This is evident since the side switch of the selector H is in Vtirst position. Not only will this be true while the side switch is in first position, but also when it is in second position, as indicated by the side switch contact points 171 and 172 being connected. The calling subscriber having thus extended his connection to the second-selector H, he operates his dial in accordance with the second digit 2, with the result that the line relay 95 is operated twice and the spring 168 carried twice into engagement with the spring 16a while the slow-acting relay 97 is energized. rllhe result is that at the tirst impulse the slow-acting private magnet relay 96 is energized and the vertical magnet 99 operated once. The slow-acting relay 96, of course, remains energized until the second impulse is sent, which again operates the vertical magnet 90 through the slow-acting relay 96. In this way the switch shaft ot the second-selector H is raised two steps by the vertical magnet 99, and the line and private wipers 178 and 174-, and 175 are placed oppositie the iirst contact of the second level ot the second-selector bank. 1t will be evident, ot' course, that as soon as the slow-acting relay 96 energizes, the springs 176 and 177 are pressed into contact and an energizingr circuit established for the private magnet 101 'from ground G through the springs 176 and 177 and through the private magnet 101 to the battery lead 128, thence through battery B to ground G. The private magnet, of course, attracts its armature, but does not release the side switch to second position until all the impulses have been sent in, atter which the slow-acting relay 96 cle-energizes, as 1n the iirst-selector F, which then interrupts the circuit between the springs 176 and 177. 1t will be seen that the energizing circuit for the vertical magnet 99 and for the slowacting relay 96 extends trom ground G6 through the line relay springs 168 and 1611, through the relay springs 166 and 168 to the private magnet relay 96, thence to the vertical magnet 99, side switch contact point 178, side switch wiper 179 to the battery lead 128, thence through battery B to ground Gr. Vxhen the side switch passes to second position the side switch wiper 179 engages the contact point 180, thus closing the energizing circuit ior the rotary magnet 100 from ground G5 through the interruptor spring 181, rotary magnet 100, side switch Contact point 180, side switch wiper 179 to the battery lead 128, thence through battery 1i to ground (i. 1t will be seen that in the selector H, as in the selector F, at the lirst impulse t-l rough the rotary magnet 100 the armature oit the private magnet 101 is oper` ated to trip the side switch to third position, provided the lirst trunk-line is idle, by which operation the subscribers line is placed in connection with the connector switch 1. However, it the first trunk-line is not idle the private wiper 175 will be carried onto grounded contacts, as described in connection with the lirst-selector F, with the result that the private magnet 101 is energ-ized and maintained energized tor the purpose oit locking the side switch in second position until the rotary magnet has advanced the shaft and wipers beyond the last busy trunk, at which time the private magnet de-energizes and permits the side switch to pass to third position, with the usual result. ln the second-selector H it will be seen that the side switch comprises the wipers 179, 161, 160, 182 and 188. The shaft wipers 178, 174 and 175 having been rotated into engagement with the trunk conductors 18%, 185 and 186, then when the side switch wipers 161 and 160, upon passing to third position, engage the side switch contact points 187 and 188 the circuit is extended to the connector switch I. The connector line relay 105 instantly energizes, the current liowing from ground GS through the winding 189 of the line relay 105 to the trunk conductor 185, rotary line wiper 1771 ot the second-selector H, Contact point 188, side switch wiper 160, over the rotary side and through the first-selector F, line switch C and telephone A to the vertical side, bach .through the line switch C, firstselector F and second-selector H to the side switch wiper 161, Contact point 187 vertical line wiper 17 8, vertical trunk conductor 1811-, winding 190 ot the line relay 105, through the release relay 106 to the battery lead 128, thence through battery B to ground G. As soon as the slow-acting relay 106 energizes it operates to shift the spring 191 trom the spring 192 and into engagement with the spring 198, and at the same time operatesto close the springs 194 and 195 in contact. As soon as the springs 1911 and 195 close in contact a guarding potential trom ground G9 is applied to the trunkrelease conductor 186, to take the place of the guarding potential removed from the private wipers 175 and 83, by the shifting ot the second-selector side switch Wiper 182 away from the contact point 172 at the instant Athat the second-selector side switch trips .to thirdv position. This guarding potential, itfwill be seen, also maintains the slew-acting :relays 97 fand 36 energized, the energising'circuits boil vj; tollows: lroin groinul. G9 at the connector l to the contact point 19.0, side switch wiper 197, trunk-releasefconductor 13G, private wiper 175, con-- ductor 193, seeondselector side switch wiper 133,1conductor 199, slowea-Lf'i' u 97 to the battery lead 123, thence through battery B to ground G. rl"he slow-acting relay S `is energized over a branch circuit as `follows: trom 'the private wiper 175 through :the side switch wiper 183 the second-seleetor H, conductor 200, trunk-release conductor 201, private wiper 83, conductor 1&7, side'switeh wiper 93, conductor 1530, through therelay 86 to the lrittery lead 12S, thence Ithrough -battery B to ground G. Theclosure 'of Contact between the release relay springs 191 and 193, it will be seen, entends connection between the line relay spr-ing 202, the vertical magnet and the rotar i magnet 109. l/Vhen the line relay 105 attracts its armature it will be seen `that the spring202 is separated from thespring 203l and `carried into engagement with the spring 204 with no result. However, when the subscriber proceeds by operating his dial ttor the .third vdigit 2, the line relay 105 operates exactly as the line relays ot the selector switches Fand H have'operated, permitting thespring 202 to tall bach onto the spring 203 a number of times corresponding to the digit. Each time that the circuit 'is closed between the springs 202 and 203 the vvertical `magnet 110 is energized once, raising the switch shal't each time. The energizing circuit through the saidmagnet, it will be seen, extends from ground G through the line `relay springs 203 and 202, through the release relay springs 191 and 193 to the vertical magnet 110, thence to the Contact point 205, side switch wiper 233, private magnet relay 107, thence through said relay to battery lead 123, and through battery B to ground G. At the first impulse the private magnet relay 107, being a slow-acting relay, remains energized during the interval in which the remaining impulses aretransuiitted to the vertical magnet llt). it the end ot this operation the shalt wipers 102, 103 and 10d will be found opposite the first contact ot' the second level ol the connector banks. lt will be seen that, upon energizing, the slow-acting private magnet relay 107 separates the springs 207 and 203, and (arries the spring 209 into engagement with the spring 210. he closure ot contact between the springs 210 and 209 energizes the vprivate magnet 113 by a flow ol1 current from ground G11 through the springs 210 and 209 land through the said private magnet 113, thence through battery into engagwmid with. the Contact points 217 213, 219, and 221. .The subscriber 5 s now ref-dy to operatehis calling device for the last digit 0. He does so and theretransmits to the central .office ten inises, thereby operating the line relay v105 Each time that the line relay ...il 1g t, e A.. @i

ten times. springs 203 and 202 engage, an energizing circuit is established through the rotary magnet 109 from ground G10 through the said springs 203 `and 202, springs 191 and 193, through the rotary magnet 109 to kthe Contact point 219, thence through the side switch wiper 206, and through the private magnet relay 107 to thev battery lead 123, thence through battery B to ground G. Again the private magnet relay'energizes, as in the previous case, remaining so until all the rotary impulses are transmitted, thereby retaining the pri-vate magnet also energized. The rotary magnet 109then-operates to rota te the shalt wipers into engagement with the desired line #2220. Ir" this line is busy the time, the connector switch will be given thefbusy release, the calling suhsifriberlis given the busy-signal, thus making 1t impossible to extend the calling line into Connection with the called line.

Before describing the results that follow when the-connector linds a busy line, the description othow a connection is-estalolished willbe completed. As soon as the line relay 105'ceases to operate tor the last digitl the `private .magnet relay 107 cle-energizes, as heretofore.explained,in this instance permiting the side switch to trip to'third position. The result is that the side switch wipers 211, 212, 206, 197 and 213 engage the contact points 221, 225, 226, 227 and 223, respectively. then the side switch wiper 213 engages the Contact `point 8 a guarding potential is extended to the private wiper 1011 'for protecting the seized line from .outside interference while theconnection is established. rllhis guarding potential extends from ground G1? to the contact point 223, thence by way of the side switch wiper 213, conductor 229 `to the vp1-ivato wiper 104. Not only does this guardingpotential prevent other connectors from .seizing the saine lineover multiples of the normal conductors 232 and 233 and 234, but it also provides means ior energizing thecutoil7 relay 123 of .the line swit-chC, whereby said switch C is prevented from operating when the called subscriber removes his receiver -trom the switch-hook 236. it willv also be seen that when the side switch passes to third position the trunk-release conductor 186 that extends from the second-selector to the connector (Figs. 1 and 2) is provided with guarding potential from ground G10 through the line relay springs 202 and 204, contact point 227 side switch wiper 197, release relay springs 194 and 195 to the trunk conductor 186. However, while the side switch is in lirst and second position a guarding potential tor this trunk 186 is provided from ground Gf. The reason for this is that the guarding potential from ground G10 is interrupted while the line relay 105 is operating, and there is some liability ot some other selector, similar to the second-selector H, stopping on the same trunk-line. After the side switch passes to third position, however, there is no such danger, and the potential is provided from ground G1" only, as stated. 0f course, when the side switch wipers 211 and 212 engage their third-position contact points 224 and 225, the calling subscribers line is placed in connection with the called sub-- scribers line over the heavy conductors shown as passing through the ringer relay springs 237 and 238 on one side and 239 and 240 on the other side. As soon as connection is thus established the ringer relay 112 is energized over the circuit established when the side switch wiper 206 engages the contact point 226,' the energizing current flowing 'rom ground G13 through the interrupter 118, through the back-bridge relay springs 241 and 242, ringer relay 112, conductor 243, contact point 226, side switch wiper 206, slow-acting relay 107 to the battery lead 128, thence through battery B to ground G. It will be seen that as the interrupter 118 revolves, the energizing circuit ot` the ringer relay 112 will be broken periodically so as not to ring the called subscriber continuously. However, as soon as the called subscriber answers, the backbridge relay 114 is energized by a flow of current from ground G12, winding 244 ot the back-bridge relay 114, conductor 245, ringer relay springs 240 and 239, side switch wiper 212, contact point 225, rotary line wiper 103, rotary normal conductor 233, rotary line conductor 246, switch-hook springs 247 and 248, impulse springs 249 and 250, transmitter 251, vertical line conductor 252, vertical normal conductor 232, vertical line wiper 102, contact point 224, side switch wiper 211, ringer relay springs 237 and 238, conductor 253, winding 254 of the backbridge relay 114, thence to the battery lead 128, and through battery B to ground G. It-wvill be seen that each time that the ringer relay is energized the springs 239 and 237 are separated Jfrom the ringer relay springs 240 and 238, thereby breaking the calling line from the called line, and pressing the springs 237 and 239 onto the springs 255 and 256 which are the terminals of the ringer generator 117. As a result ringing current is sent over the called line for energizing the bell 257 while the springs 247 and 258 are in contact. Once the back-bridge relay 114 is energized, however, the energizing circuit tor the ringer relay 112 is interrupted at a point between the springs 242 and 241, thus making it impossible Jfor the ringer relay to energize as long as the called subscriber is on the line. The subscribers being thus connected, they may communicate over the main talking conductors indicated by the heavy lines and including on one side the condenser 115 at the connector I and on the .other ide the condenser 116. This talking circuit also includes the windings 77 and 78 ot the trunk coil 76. For the purpose of clearing the talking circuit of the impedance of these coils the condensers 259 and 260 are arranged across the said windings, as shown.

I will now describe the use of the master switch D and its operation. 1t was assumed in the beginning that the master switch wiper 68 was resting on the bank contact 73 and, therefore, that the plunger 38 was opposite the bank 'jack E. The calling subscriber then removed his receiver, causing the line switch to operate, which, as cxplained, throws the springs 49 and 50 into contact as a result, and the bank contact 73 is placed in connection with the nongrounced terminal of battery B through the release magnet 20 of the line switch C. This circuit, it will be seen, extends from the non-grounded terminal of battery B to the battery lead 128, thence through the release magnet 20, and through the said bank springs 50 and 49 to the bank contact 73 (see F ig. The wiper 68 maintaining the contact 73 in electrical connection with the common member 69, a circuit is established which extends through the relay 56, by way ot the said wiper 68, to the member 69, thence through the winding 262 ot' the relay 56 to ground G16, and back 'to battery B. rEhe relay 56, upon energizing, closes the springs 57 and 58 in contact, thereby closing an energizing circuit tor the rotary magnet trom ground G17 through the springs 58 and 57, interrupter springs 59 and 60 and rotary magnet to the battery lead 128, thence through battery -3 to ground G. rthe said rotary magnet then operates to rotate the ratchet wheel 64 one step, thereby advancing all idle plungers in locking engagement with the plunger shaft 42 to a position opposite the second bank jack, and advancing the wiper 68 into engagement with the second contact 263. It the trunk-line corresponding to this bank contact 263 is idle, the energizing circuit for the rotary magnet relay 56 is at once interrupted, so

that the master switchdees not advance any further.V If, however, the next trunk-line is busy, the contact 263 will be found connected with the non-grounded terminal of battery fB exactly the contact 73 has been described, and, of course, the relay .30 cannot be deenergized, but maintains vthe energizing circuit through the rotary magnet un'tilthe wiper 68 is advanced into engagement with some Contact which is not protested. The master switch is thus advanced one step each time a` subscribers line switch seizes aftrunl-line, until the wiper G8 is carried onto the last contact 2011, clearing the spring 72, as shown in F ig. fr. Then the next subscriber maires a call the pin clears the Acani 67 and the wiper 08 is caused to jump-bach over the upper side of the spring 7:21until said spring 'T2 `is cleared, at which instant the wipe-r GS again springs bach onto 'the first contac't''. Of course, if this contact fis busy the relay will enercize the rotary magnet 55 in a manner and for the purpose already explained. It will be apparent,- t-hen, that if the subscriber il has ref leased before the wiper 68 reaches the first Contact 73again, the plunger 3S will be free to fall baol-:into locking engagement with the shaft l1. It should be understood that the plunger 38 and the plunger shaft Lil are so light that even during the quick pas. age of the wiper 68 from the last Contact 04tto 'thelir'st contact 73, any plunger 38 that has been `rek-eased will be caught and retained by the plunger shaft 4:1. After the subscribers are through talking, if the calling subscriber hangs up his receiver he opens up 'the line circuit at a point between the springs and 10, thereby initiating the r^- lease 4of all of the switches. This release isas follows: Att the instant that the circuit is broken between the said springs 15 and 10, the double-wound trunk relay 76 cle-energizes, l'i'erinitting the springs 14.0 and lll under itscontrol to come into contact. This establishes an energizing circuit for the re lay 79'ov`er a path extending from ground tit through the relay 70, through the springs 1111 and 14.0 to the banl; spring 4:0, thence through-the release magnet of the line switch C tothe lmtteiv7 lead 128, thence through battery Bto ground G. As soon as the rela-y 79 draws the springs 205 and 200 into Contact -a release circuit is established through the release magnet :20, said circuit extending ffroin ground through the intenpter 80 and through the s, g 5 and 20G-to the line switch bank springs and 50. thence through the release magnet 20 to the battery lead 128, 'thence through battery B to ground G. lt will be seen that the release magnet will then ener anchas previously explained, cause the rrp armature to fall over the plunger erin 31 whereb i the members 37 and 30 engage (see F ig. 8). As the interrupter 80 tinues to revolve, the release circuit is broken for an instant, which permits the release magnet 20 of the line switch C to deenergize, thereby withdrawing the plunger 38 from the bank jack Ars a result the bank springs and 50, well as the other baul; springs of die line switch C, are separated, thus preventing any further electrical impulses from coming in from the trunli. At the saine time the line relay 105 and the release relay 106 of the `connector l energize, being in series with each other'and with the line. At the instant that the slowacting relay 10.6 and the line Vrelay 105 de energize, the energizing circuit for the re lease magnet 111, is closed at a point tween the springs 101 and 192, vand at another point betweenthe springsQOQ and 203. A iiow of current is, therefore,s'et up from ground G10 through the springs 203 and 202, through the springs 191 and 192 to the release magnet 111, thence through said inagnet to the olf-normal spring 267, to the con tact point 268 and to the battery lead 125, thence through battery B to ground G. The release magnet instantlyreleases the connector switch shaft and side switch, thereby breaking' the energizing circuit through the baclnbridge relay 11e, if the called .sub-- scriber has not in the *nean'tiine restored his receiver, and also vthe eneroizing circuit through the bridge-cut-oif relay 123 of the called line switch C. As soon as the connector switch shaft reaches its lowest position it breaks the circuit for `the release magnet 111 by separating the olf-normal spring 20T from the Contact point Q08, at which instant the release magnet of the coin nector is also-restored. The operation of the line relay 105 and of the slow-acting relay 100 not only causes the release of the cennector, as described, but also the release of the preceding switches, because the ground connection from ground G9 to the trunierelease conductor 185 Ais interrupted by both of these relays. Since the release relays 80 and 97 are dependent upon that ground tor their energized condition, as already explained, it follows that they will fall bach with the following results: As soon as the release rela.)7 97 of the second-selector Hdeenergizes, the spring 106 falls bach into non inal engagement with the spring 16T, there by closing an energizing circuit for the release magnet 98 from ground GG through the springs 10B and 164-, and through the springs 160 and 10i' to the release magnet 0S, thence to the contact point offenerinal-spring 2.70 to the battery lead thence through battery B to ground G. #is soon as the release magnet 98 energizes, the second-selector side switch and switc shaft are restored, which switch shaft, upon reaching its lowest position, opens up a release lll) circuit at a point between the oi-nori'nal spring 270 and the Contact point Q69, waereby the release magnet 98 is also restored. `When the release relay 8G ot the selector F de-energizes, the springs 137 and 138 are brought into Contact, and as a result the energizing circuit tor the release nia 'et 89 is closed. The energizing current 'tor this release magnet 89 then flows trom ground G4 through the springs 13-1 and 135, and through the said springs 137 and 13S ot the release magnet 89, thence through said magnet to the contact point 271, oli-normal spring 272 to the battery lead 128, thence through batter f B to ground G. The release magnet, upon energizing, then restores the first-selector side switch and switch shaft, which switch shaft, upon reaching its lowest position, opens the energizing circuit 'for the release magnet 89 at a point between the oli'- nornial spring 272 and the Contact point 271. Alter the switches are thus restored, the calling subscriber can, ot course., then proceed to malte another call.

Returning now to that stage of the call where the calling subscriber was operating the connector switch in accoroaiureA with the last digit 0, Vit will now be explained what taires place in the erent that the desired line is busy. iiilhen the line :ft2/'90 is calling, or when it has been called by someone. else, the private bank contacts in which the normal conductor 23st terminates are connected to ground. li another connector switch has called the line, this guarding potential would be supplied through the connector switch ifroin a ground tern'iinal similar to the ground terminal G1? in the connector switch l, as already explained but it' the line switch C is calling, a guardingl potential is established irom ground G18 through the bank springs 273 and 27st to the private normal conductor thence to the private bank contact. In a similar inanner `he line switch C protects the calling line A when the banl-I springs 4:7 and 4:8 come into contact troni ground G2, from wnich ground connection is established through the said bank springs to the private normal conductor 275. Therefore, when thc subscriber sends in the last impulse the private wiper lOlA is carried onto the grounded contact, and when the slow acting relay 107 ol' the connector de-energizes, the springs 207 and 208 engage, closing an energizing circuit through the release magnet 11.1. 'lhis circuit extends from the grounded private bank Contact to the private wiper side switch wiper 213, contact point 221, springs 207 and S, release magnet 111, normal springs 267 and 20S to the battery lead 18, thence through battery B to ground G. `he connector release magnet, upon energizing, operates to restore the switch to normal position, whereby the normal springs 267 and 268 are disengaged, destroying the energizing circuit o't the release magnet. The springs 28,1 and 282 are pressed into Contact when the shaft returns to normal position, thus connecting the bus -signaling circuit with the calling sub- Si the primary winding ot the busy coil 110 through the springs 282 and 281 to the rotar f line conductor 185, tirough the substation to the Vertical side of the line, then over said vertical side back to the. connector l, through the winding 1913 ot' the line relay 105 to the relay 106, and through battery B to ground thence to the interrupter ground G20, through the interrupter 1:20 to the primary winding oic the busy coil 119 back to the secondary winding. When the calling subst iber receives the busy-signal he understands that the line is busy and hangs up his receiver, The line circuit is open, as already explained, with the result that the line and slow-acting relays 105 and 106 ot the connector l de-energize, causing the release. ot the connector and all other switches,

heretoforeexplained.

From the 'foregoing description it will be evident that il the line switch C should be tripped onto the trunk that terminates in the iirst-ijzeleetor F, and it the conductors le ding trom the line switch banlr springs au or 51 should be broken, the line switch tl will instantly be released for the Jollowing prisons: Unless the trunk condurtors 7l and 75 leading from the said springs 525 and 51 are intact, it will be impossible to energize 'the trunk relay 77; consequently the trunk relay springs lil-0 and 141 would remain in contact after the bank springs slt) and engage, and the release relay 79 will energize. througlrthe springs 14-1 and 140, and Ll0 and 50, as already explained, with the result that the release circuit through the release magnet E20 ol the line switch C is established Yfrom ground G15 through the interruptor S0 and through the springs Q60 and 205, springs slt) and 50, through the release magnet 20, and through said magnet to the battery. rEhe effect ot establishing this release circuit producing the release ot the line switch C. T he same is true with regard to the vfirst-Selector F-that is, if the first-selector F stops on the trunk-line leading to the second-selector H, for example, and this trunk-line happens to be open-that is, it either of: the trunlr conductors 153 or 154C are openthe release relay 86 cannot be maintained energized, because the line relay 95 of the second-selector H cannot energize, since the line is open, and since the line relay 95 cannot energize the line relay springs 163 and 165 are not brought into contact to supply ground to the trunk-release conductor 201 for maintaining the release relay S6 enerioers line Conductors as follows: fromA has already been described as llt) Ythe seeondsele Qositron.

also he seen-that the' trunlr` relay tained. energized through the line relay 95 1,5ea,soe

gleed. Therefore, as soon asvthe release relay -de energi... the release magnet 89 will then cnergiye, as heretofore explained, with the result vtl at the switch is restored. It, will he seen that the release magnet- 89 et. necessity energi/cs, since at the time the switch sha-'tt is oil" normal the' oil-normal .spring 272; is. in engagement with the con- `selector l? Ybe released, but the line switch l iifl'l likewise la'e released at the instant that side switch trips to third ce in that ere-nt the trunlr relay 7.7 fle-energizes, beca o the-open line be.- tween` `the selector l? and` tie selector H. lt will` therefore be seen that an open trunk between a tirstselecuor and a second-seiector will cause the release ot all switches up te :that point, it the -rst-selector seizes the said open. trunk. Also, il the trunk-release vconductor 201 running from. the first-selector F to the second-selector .H is open when the first-selector stops on the trunk, it will be seen that the Erst-selector l" will be released, because there is no connection to .relay 7l' is retained energized through the line rel-ay Met-the first-selector l". twill 77 is mainby theA second-selector H during the short interval that the first-selector ll" is permitted' toj. remain in engagement with the trunk. The same is true ot the second-selectorv H-e-:that is, it either ot the trunk conductors 184- or L85 is open as soon as the see.- ond-selector H seizes the trunk-line, then all ot the switches-that is, the second-selector H, the inst-selector F and the line switch (-*will be released. Also, it' the trunk-release conductor 186 is open, the second-selector H and the first-selector F will be released, because the release relays 97 and S6 cannot be maintained energized. These release relays, ot course, while cle-energized close a circuit between the release magnet and one of the line. relay springs. For eX- ample, the release magnet 89 is connected with the line relay spring 135, and the release magnet 98 is connected with the line relay spring' 164. Whenever the line relays 84 and 95 are de-energized, these springs 135 and 164 are, ot' course, connected to lground. lt is tor preventing a premature release hatthe release relays are energized as soon the l'ne relays are energized, and this,

olfv coure, occurs at the instant that the switch is seized, as has been explained.

ln connection. with this system l electto 'c one level oli the secondfselectors for i' poses than picking ont connectors. n lthis case l .-rilireserve the tenth level ol 'eason the second-selector e the. shalt wipers tothe e seco. heele-eter then roichs ont an t *lr Yhe condnctors which terminate in shown in '5. fis soon as co1 iection is established with the .said trani/ifi;ie-that is, as soon as the selector side switch nass-es to third position. the line relay i385, similar to the line relay or" the second-selector lil, energises. lay

Y The said rethen operates to press they springs 287,

and i289 into, Contact, the spring` 287 be'- grounded. ils soon as these .springs contact the trunk-release conducis connected topgronnd G21 for the purpose ot maintaining, the release relays of the selector switches F and lvl energized.

At the same time a signal lamp 290 is energized by a flow 01': current from groundl G21 through the springs 287 and 288 to the lamp S390, thence through the springs 291 and 292 ot the .jack .l Vto the battery lead 12S, thence tlniongaibattery B to gro-und G. The opera-tor who is thereby `given a Signal answers by plugging into the 'jack J, separatingthe springs 291 and 292 and extinguishing the m5 it 290. lt will he seen that at any time calling subscriber wishes to release he simply hangs np his receiver, asheretotore., Lhereby vopening' up the line circuit. Asa esltthe line relay 286 (Fig. 6) cle-enerand permits the springs 287, 288 anc .a99 to separate, thereby removing ground troni the trunk-release. conductor 5, whereby the release et all the switches is initiated. The cle-energizing ot the said line relay also removes ground from the lamp 290, so that 1when the operator withdraws her plug the lamp will not be lighted; or, in the event that the operator has already withdrawn her plug, the lamp 290 will go out.

From the foregoing it will be seen that I provide an improved two-wire automatic telephone exchange trunlring system-that is to say, a system in which no operating grounds are employed at the substation, the two wires ot the subscribers lines being sufiicient tor controlling all ot the operations at the exchange or central station, and

no third conductor being necessary outside ot the said exchange or central station. This I accomplish without the necessity of providing special high resistance coils at the substations, and without employing more than two trunk conductors leading to each first-selector. Trunks having third concluetors are employed between the lirst-selectors and the second-selectors, and between the second-selcctors and the connectors; but any established connection from a calling substation is tree from ground and ot a twowire character until it reaches the lirstselector. Furthermore, the selectors and connectors are each provided with only one double-wound line relay, as distinguished `from the old arrangement which involved a pair ot line relays ttor each selector and each connector. Again. it will be seen that I provide subscribers` individual preliminary trunlring switches that are each adapted to auton'iatically restore itself it placed or lett ott normal when the subscribei"s line is in normal condition-that is to say, when the line is open or not in use. In addition, it will be seen that I provide a two-wire system in which provision is made tor trunlting to an operatoria manual board tor any desired purpose. No operating grounds or special high resistance coils are employed at the subscribers substations, and the battery current for talking purposes is supplied to the substations over the metallic or two-wire circuits provided therefor.

What I claim as my invention is 1. In a telephone system` a connector switch having a line relay and a slow-acting relay in series therewith for controlling all the connecting and releasing operations ot the said switch.

2. In an automatic. switch, a line relay responsive to controlling impulses, a slow acting relay connected in series with said line relay but irresponsive to such impulses, operating means for said switch controlled loy said line relay, and restoring means for said switch controlled by said slow relay.

S. In an automatic switch, a line relay responsive to controlling impulses, a slow acting relay connected in series with said line relay but irresponsive to such impulses, and operating and restoring means for said switch each jointly controlled by said relays.

Ll. In a telephone system, a. trunk line extending to a manual connective terminal. a signaling device associated with said terminal, means including an automatic switch controlled over the two sides of a calling li e in series for etei'iding a connection to said trunk line, a, holding circuit including a non-talking conductor ot said trunk line tor retaining said switch in operated position, and a relay bridged across said trunk line in series with the exchange battery tor controlling said holding circuit and said signaling device.

5. In a telephone system, an individual line switch of? the type which is adapted to remain in operatef position when operated, independent olf' the energization of any magnet, a selector adapted to be seized by said line switch, said selector being ot the type which requires substantially continuous closure ot the line circuit to maintain it in operated position, a release magnet tor said line switch, and means individual to said selector and responsive to a sustained open ing ot the line circuit for operating said release magnet.

6. In a telephone system, a trunk line, a subscribers individual line switch 'for eX- tending a connection tosaid trunk line` a release magnet tor said line switch, a circuit for said magnet including an automatic interrupter, and means controlled over said trunk line for closing said circuit.

Signed by me at Chicago, Coolr County', Illinois, this 25 dav ot January. 1908.

EDVARD A. MELLINGER. 

